Steel alloy tubes

ABSTRACT

Low carbon steel alloy tubes of high tensile strength. The steel alloy contains less than 0.23% carbon, less than 0.5% silicon, from 1.00 to 1.50% manganese, less than 0.040% phosphorus, less than 0.040% sulfur, less than 0.30% copper, less than 0.50% chromium, from 0.010 to 0.080% aluminum, and the remainder of iron and impurities in an amount and variety which do not impair the desired characteristics of the alloy. There is preferably not less than 0.20% silicon and from 1.00 to 1.35% manganese. This steel after being rolled into a steel plate is welded into a steel tube of high tensile strength. Also, the steel alloy is a killed steel and in particular an aluminum killed steel.

[73] Assignee:

United States Patent Kikkawa et al.

[54] STEEL ALLOY TUBES [72] Inventors: Osamu Kikkawa; Akira Kambayashi,both of Yokohamashi, Japan Nippon Kokan Kabushiki Kaisha, Tokyo, Japan[51] Int. Cl ..B2lc 37/00 [58] Field of Search ..75/124, 125; 29/193 [56] References Cited UNITED STATES PATENTS 8/1890 Blakey ..29/193 [1513,656,917 [4 1 Apr. 18, 1972 Breeler Primary Examiner-l-lyland BizotAn0rneySteinberg and Blake [5 7] ABSTRACT Low carbon steel alloy tubesof high tensile strength. The steel alloy contains less than 0.23%carbon, less than 0.5% silicon, from 1.00 to 1.50% manganese, less than0.040% phosphorus, less than 0.040% sulfur, less than 0.30% copper, lessthan 0.50% chromium, from 0.010 to 0.080% aluminum, and the remainder ofiron and impurities in an amount and variety which do not impair thedesired characteristics of the alloy. There is preferably not less than0.20% silicon and from 1.00 to 1.35% manganese. This steel after beingrolled into a steel plate is welded into a steel tube of high tensilestrength. Also, the steel alloy is a killed steel and in particular analuminum killed steel.

6 Claims, No Drawings STEEL ALLOY runes CROSS REFERENCE TO RELATEDAPPLICATION This applicationis a divisional of our application Ser. No.

683,720, filed May 16, 1967, for Steel Alloy and Tube ManufacturedTherefrom now U.S. Pat. No. 3,554,734.

BACKGROUND OF THE INVENTION The present invention relates totubes madeof low carbon steel alloys of high tensile strength. While the alloyshave many possible uses, the same are particularly useful for themanufacture of welded steel tubes. The alloys which are used inmanufacturing the steel tubes according to the present invention are ofX-60 high tensile strength.

At the present time there are known steel alloys of X-60 high tensilestrength used in the manufacture of steel tubes, but these alloysrequire as part of their composition columbium or vanadium, or both, inaddition to manganese. According to the provisions of API (1966), it isspecified that such alloys should contain less than 0.26% carbon, lessthan 1.35% manganese, less than 0.04% phosphorus, less than 0.050%sulfur, more than 0.01% Cb and more than 0.02% V. In addition it isspecified that either one or both of Cb and V should be included in thealloy.

Inasmuch as steel alloys of this type are manufactured primarilyaccording to the semi-killed method, these alloys do not have the finegrain structure of an alloy of high carbon content, and as a result theyare required to be rolled under special lowtemperature rollingconditions. As a result the efficiency with which the rolling operationsare carried out with conventional alloys of this type are considerablybelow an ideal rolling efi'lciency. Furthermore, because of the carboncontent, which is relatively high, the capability 'of welding the alloy,in the field is poor. Also, because the alloy is a semikilled steel, itsstrength is not uniformly distributed.

. SUMMARY OF. THE'INVENTION It is accordingly a primary object of thepresent invention to provide tubes made of steel alloys which avoid theabove drawbacks of the conventional steel alloys.-

It is a further objectof the invention to provide tubes made of lowcarbon steel alloys of high tensile strength, which alloys do notcontain relatively expensive columbium and/or vanadium, but insteadreplaces the columbium and/or vanadium with less expensive substanceswhile at the same time providing an increase inthe desirablecharacteristics of the alloys.

It is yet a further object of the present invention to provide weldedsteel tubing made of these alloys and particularly of killed steel, andmost preferably aluminum killed steel alloys.

With the above and other objects in view, the present invention mainlycomprises tubes made of low carbon steel alloys of high tensilestrength, which contain manganese, copper, and chromium, the relativelyinexpensive copper and chromium being used to replace the far moreexpensive columbium and vanadium, while at the same time achievingsuperior results. This alloy of the invention is rolled into steel platewhich is then welded into steel tubing by a suitable welding methodsuch'as the UOE submerged arc welding method. In this way it is possibleto provide steel tubes of X-60 high tensile strength, having in fact atensile strength of more than 78,000 psi. The chemical composition ofthis low carbon steel alloy of the invention includes less than 0.23%carbon, less than 0.50% silicon, from 1.00 to 1.50% manganese, less than0.40% phosphorus, less than 0.040% sulfur, less than 0.30% copper, lessthan 0.50% chromium, from 0.010 to 0.080% aluminum, and the remainder ofiron and impurities the quantity and variety of which do not impair thedesirable characteristics of the alloy.

' In this way the strength of the low carbon steel alloy of the presentinvention having the above chemical composition is increased to thedesired extent while utilizing inexpensive copper and chromium ratherthan the far more expensive columbium and vanadium. In addition, thecutting toughness of the alloy is improved and the desiredcharacteristics thereof are stabilized by manufacturing the alloyaccording to the aluminum killed method.

As compared with conventional alloys of the above type containingcolumbium and vanadium, the carbon content of the alloy of the inventionis substantially reduced so as to improve greatly its weldability. Inaddition, there is achieved with the alloy of .the invention a finegrain structure which makes it possible to avoid the reduction inefl'iciency of the rolling operations necessarily inherent in theconventional alloys as a result of the temperature controls required dueto the critical quantities of the various elements in the conventionalalloys.

While the carbon content of the alloy of the invention is less 5 than0.23 percent, the minimum quantity of carbon is 0.10

percent in view of the value of carbon equivalent.

Inasmuch as silicon is included to provide the required strength for thematerial, the maximum quantity thereof should be 0.50 percent while theminimum quantity should be 0.20 percent. Otherwise the required strengthis not achieved.

As is the case with conventional steel alloys, it is preferred that thequantities of sulfur and phosphorus should be quite low, but it wasfound that no deleterious effects were noted where the quantities forboth of these elements did not exceed 0.040 percent.

Inasmuch as copper if present in an amount. greater than 0.30 percentcauses reheat brittleness during the rolling operations while chromiumin a presence of more than 0.50 percent will in general result in anincrease in the hardness of the material in view of the value of carbonequivalent, resulting in difficulties in connection with weldingoperations, the composition of the invention contains less than 0.30percent copper and less than 0.50 percent chromium.

. Because the granulation resulting from the presence of aluminum is notnoticeable up to 0.010 percent, whereas cracks in the steel ingot willresult where the aluminum is present in a quantity of more than 0.080percent, the aluminum in the alloy of the invention is maintainedbetween 0.0l0percent and 0.080 percent.

Manganese in an amount of less than 1.00 percent does not provide therequired strength while manganese in an amount of more than 1.50 percentimpairs the weldabilityof the alloy, in much the same way that chromiumimpairs the weldability thereof if present in too great an amount. Themanganese is maintained between 1.00 and 1.50 percent, preferably from1.00 to 1.35 percent.

' DESCRIPTION OF A PREFERRED EMBODIMENT The manner in which the presentinvention brings about the desired objects will be understood more fullyfrom a consideration of the following preferred embodiment of theinvention.

In accordance with the invention a steel tube of high tensile strengthwas manufactured by the above-discussed methods, namely by manufacturingthe steel according to the aluminum killed process and then rolling thesteel into the form of steel plate. The low carbon steel alloy of theinvention contained 0.l5-0.20% carbon, 0.20-0.50% silicon, 1.00-1.35%manganese, 0.10-0.20% copper, and 0.10 and 0.40% chromium.

The strength, cutting toughness, weldability, inequality of strengthdistribution, anti-corrosive property and similar properties of a tubemanufactured according to the submerged With respect to preservation ofstrength (durability), the tube manufactured with the alloy of theinvention and those manufactured with the conventional alloys showed ingeneral the same tensile strength of more than 60,000 psi.

2. Cutting toughness:

The tubes manufactured with the conventional alloys had 50% shearrupture temperature (50% fracture surface transition temperature) of 30to +40 F., while the alloy steel of the present invention showed animproved 50% shear rupture temperature of 80 to -60 F.

3. Weldability:

The steel alloy of the present invention had a weldability comparable interms of carbon equivalent (USA) to alloys containing 0.330.49%columbium or 0.35-0.45% vanadium. Thus, without using these latterexpensive materials the alloy of the invention achieved weldabilitywhich could only be achieved with alloys having relatively large amountsof these expensive materials.

4. Rolling efficiency:

Because of the temperature controls required by the conventional alloysthere is a decrease in the rolling efficiency with the conventionalalloys on the order of whereas there is absolutely no decrease in therolling efficiency when rolling the alloy of the present invention.

5. Inequality of strength distribution:

With the convention steel alloys manufactured according to thesemi-killed process, the inequality of strength distribution was foundto be 6-7 Kglmm while with the steel alloy of the present inventionprepared according to the killed process the inequality of strengthdistribution was reduced to 4-5 Kg/mm.

6. Anti-corrosive property:

A comparison of the alloy of the invention with the conventional alloysshowed a marked improvement in the anti-corrosive property. Inparticular, the extent of corrosion of the steel alloy of the inventionwas less than 10 percent, and this latter amount represented a markedimprovement over the anti-corrosive properties of the conventionalalloys.

it is apparent, therefore, that with the present invention it ispossible to achieve a low carbon steel alloy of high tensile strengthparticularly suitable for the manufacture of steel tubes, althoughequally suitable for the manufacture of other articles, by making use oflow carbon steels which have as part of their composition copper andchromium instead of making use of high carbon steels which have as partof their composition expensive columbium or vanadium. Using the lowcarbon steel of the alloy of the invention greatly improves theweldability as compared to the conventional alloys. in addition, thegranulation is brought about by way of the aluminum-killed method usedin manufacturing the alloy of the invention instead of during therolling operations, as has been conventional, so that not only is theefficiency of the rolling operations improved but in addition the degreeto which the inequality of the strength is distributed is decreased. Itis-therefore possible with the alloy of the invention to achievearticles such as steel tubes having high tensile strength and very highquality while utilizing an alloy and methods which are simple andinexpensive as compared to conventional alloys and methods.

While in the above-described embodiment relates to the production of aparticular high tensile strength steel tube, it is to be understood thatvariations and modifications of the alloy can be made within the limitsof the invention without departing from the spirit or scope of theinvention. Such variations and modifications are accordingly meant to becomprehended within the meaning and scope of equivalents of theappendedclaims.

What is claimed is:

1. Welded Steel tube of high tensile strength, said tube being made of asteel alloy consisting essentially of between about 0.1% and less than0.23% carbon, between about 0.20% and less than 0.50% silicon, about1.00 to 1.35% manganese, less than 0.040% phosphorus, less than 0.040%sulfur,

between about 0.10% and less than 0.30% copper, between about 0.10% andless than 0.50% chromium, about 0.0l0-0.080 aluminum, and the balancesubstantially of iron.

2. Tube according to claim 1 wherein said' tube is a welded tube.

3. Tube according to claim 1 wherein said steel alloy is a killed steel.

4. Tube according to claim 3 wherein said alloy is an aluminum killedsteel.

5. Tube according to claim 1 wherein the amount of manganese is about1.00 to 1.35%.

6. Tube according to claim 1 wherein said alloy contains 0.15-0.20%carbon, 0.20-0.50% silicon, l.0-l.35% manganese, 0. l00.20% copper, and0. l00.40% chromium.

2. Tube according to claim 1 wherein said tube is a welded tube.
 3. Tubeaccording to claim 1 wherein said steel alloy is a killed steel.
 4. Tubeaccording to claim 3 wherein said alloy is an aluminum killed steel. 5.Tube according to claim 1 wherein the amount of manganese is about 1.00to 1.35%.
 6. Tube according to claim 1 wherein said alloy contains0.15-0.20% carbon, 0.20-0.50% silicon, 1.0-1.35% manganese, 0.10-0.20%copper, and 0.10-0.40% chromium.